In a communication system which employs multiple satellite antennas which project communication beams onto the surface of the earth, a group of receive antenna beams must be switched or routed from receiving antennas to one or more available tuners. These tuners downconvert the signals from the receiving antennas in order to extract the information conveyed by the received signals. This information can represent analog or digitized voice, analog or digitized video, facsimile data, and so on. In some communication satellite architectures, as many as 50 or 100 antenna beams must be simultaneously routed to one or many tuners. Therefore, because of the requirements of the satellite system to switch between tuners and antenna beams, switch matrices are employed to perform this function. Generally, these switching matrices must operate at radio frequencies and higher.
Radio frequency switch matrices are generally embodied as large three-dimensional structures. Crossbar switches may be used at higher frequencies, but can be rendered less effective due to the need for directional couplers used to multiplex signals from one or more input pathways to one or more output pathways. Additionally, at some frequencies (such as below 3.0 GHz) their use may be impractical due to the large volume required to implement a directional coupler which operates in this frequency range. The problem is compounded in that multiple switch matrices are often required in order to meet the capacity needs of the particular communication system.
Additionally, future communication systems will demand that switch matrices be calibrated to within one dB of the desired gain in order to maintain transmit and receive beam-to-beam isolation requirements. With current radio frequency technology, it is impractical to manually align or to expect manufacturing tolerances of one dB in large switch matrices. Further, maintaining a flat frequency response over a large bandwidth can dramatically increase the cost and complexity of a radio frequency crossbar switch used in either transmit or receive communications modules.
Therefore, what is needed is an inexpensive radio frequency switch matrix capable of operating over a wide bandwidth which provides a multiplexing function without requiring a large amount of weight and power. What is also needed, is a radio frequency switch matrix that can be quickly and automatically calibrated with a minimum number of calibration coefficients.